In Situ Formed Li-Ag Alloy Interface Enables Li10GeP2S12-Based All-Solid-State Lithium Batteries

Dual-Component Interlayer Enables Uniform Lithium Deposition and Dendrite Suppression for Solid-State Batteries

β-Lithium thiophosphate (LPS) exhibits high Li+ conductivity and has been identified as a promising ceramic electrolyte for safe and high-energy-density all-solid-state batteries. Integrating LPS into solid-state lithium (Li) batteries would enable the use of a Li electrode with the highest deliverable capacity. However, LPS-based batteries operate at a limited current density before short-circuiting, posing a major challenge for the development of application-relevant batteries. In this work, we designed a dual-component interfacial protective layer called LiSn-LiN that forms in situ between the Li electrode and LPS electrolyte. The LiSn component, Li22Sn5, exhibits enhanced Li diffusivity compared with the metallic lithium and facilitates a more uniform lithium deposition across the electrode surface, thus eliminating Li dendrite formation. Meanwhile, the LiN component, Li3N, shows enhanced mechanical stiffness compared with LPS and functions to suppress dendrite penetration. This chemically robust LiSn-LiN interlayer provides a more than doubled deliverable critical current density compared to systems without interfacial protection. Through combined XPS and XAFS analyses, we determined the local structure and the formation kinetics of the key functional Li22Sn5 phase formed via the electrochemical reduction of a Sn3N4 precursor. This work demonstrates an example of the structural-specific design of a protective interlayer with a desired function - dendrite suppression. The structure of a functional protective layer for a given solid-state battery should be tailored based on the given battery configuration and its unique interfacial chemistry.

Deeply Lithiated Carbonaceous Materials for Great Lithium Metal Protection in All-Solid-State Batteries

Protection of lithium (Li) metal electrode is a core challenge for all-solid-state Li metal batteries (ASSLMBs). Carbon materials with variant structures have shown great effect of Li protection in liquid electrolytes, however, can accelerate the solid-state electrolyte (SE) decomposition owing to the high electronic conductivity, seriously limiting their application in ASSLMBs. Here, a novel strategy is proposed to tailor the carbon materials for efficient Li protection in ASSLMBs, by in situ forming a rational niobium-based Li-rich disordered rock salt (DRS) shell on the carbon materials, providing a favorable percolating Li+ diffusion network for speeding the carbon lithiation, and enabling simultaneously improved lithiophilicity and reduced electronic conductivity of the carbon structure at deep lithiation state. Using the proposed strategy, different carbon materials, such as graphitic carbon paper and carbon nanotubes, are tailored with great ability to speed the interfacial kinetics, homogenize the Li plating/stripping processes, and suppress the SE decompositions, enabling much improved performances of ASSLMBs under various conditions approaching the practical application. This strategy is expected to create a novel roadmap of Li protection for developing reliable high-energy-density ASSLMBs.

Insight into Dendrites Issue in All Solid-State Batteries with Inorganic Electrolyte: Mechanism, Detection and Suppression Strategies

All solid-state batteries (ASSBs) are regarded as one of the promising next-generation energy storage devices due to their expected high energy density and capacity. However, failures due to unrestricted growth of lithium dendrites (LDs) have been a critical problem. Moreover, the understanding of dendrite growth inside solid-state electrolytes is limited. Since the dendrite process is a multi-physical field coupled process, including electrical, chemical, and mechanical factors, no definitive conclusion can summarize the root cause of LDs growth in ASSBs till now. Herein, the existing works on mechanism, identification, and solution strategies of LD in ASSBs with inorganic electrolyte are reviewed in detail. The primary triggers are thought to originate mainly at the interface and within the electrolyte, involving mechanical imperfections, inhomogeneous ion transport, inhomogeneous electronic structure, and poor interfacial contact. Finally, some of the representative works and present an outlook are comprehensively summarized, providing a basis and guidance for further research to realize efficient ASSBs for practical applications.

Synergistically Stabilizing Thin Li Metal through the Formation of a Stable and Highly Conductive Solid Electrolyte Interface and Silver-Lithium Alloy

In this study, a stable solid electrolyte interface (SEI) and a Ag-Li alloy were formed through a simple slurry coating of silver (Ag) nanoparticles and Li nitrate (LiNO3) on a Li metal surface (AgLN-coated Li). The Ag-Li alloy has a high Li diffusion coefficient, which allowed the inward transfer of Li atoms, thus allowing Li to be deposited below the alloy. Moreover, the highly conductive SEI enabled the fast diffusion of Li ions corresponding to the alloy. This inward transfer resulted in dendrite suppression and improved the Coulombic efficiency (CE). The AgLN-coated Li exhibited an initial capacity retention >81% and CE > 99.7 ± 0.2% over 500 cycles at a discharge capacity of 2.3 mA h cm-2.

Combining Solid Solution Strengthening and Second Phase Strengthening for Thinning Li Metal Foils

Thin lithium (Li) metal foils have been proved to be indispensable yet elusive for practical high-energy-density lithium batteries. Currently, the realization of such thin foils (<50 μm) is impeded by the inferior mechanical processability of metallic Li. In this work, we demonstrate that the combination of solid solution strengthening and second phase strengthening, achieved by the addition of silver fluoride (AgF) to Li metal, can substantially enhance both the strength and ductility of metallic Li. Benefiting from the improved machinability, we succeed in fabricating an ultrathin (down to 5 μm), freestanding, and mechanically robust Li-AgF composite foil. More interestingly, the in situ-formed LixAg-LiF skeleton in the composite facilitates Li diffusion kinetics and uniform Li deposition, where the thin Li-AgF electrode displays a prolonged cycle life over 500 h at 1 mA cm-2 and 1 mAh cm-2 in a carbonate electrolyte. Coupled with a commercial LiCoO2 cathode (3.4 mAh cm-2), the LiCoO2||Li-AgF cell delivers a notable capacity retention of ∼90% over 100 cycles at 0.5 C with a low negative/positive ratio of 2.5.

LiAlO2-Modified Li Negative Electrode with Li10GeP2S12 Electrolytes for Stable All-Solid-State Lithium Batteries

Lithium (Li) metal has an ultrahigh specific capacity in theory with an extremely negative potential (versus hydrogen), receiving extensive attention as a negative electrode material in batteries. However, the formation of Li dendrites and unstable interfaces due to the direct Li metal reaction with solid sulfide-based electrolytes hinders the application of lithium metal in all-solid-state batteries. In this work, we report the successful fabrication of a LiAlO₂ interfacial layer on a Li/Li₁₀GeP₂S₁₂ interface through magnetic sputtering. As LiAlO₂ can be a good Li⁺ ion conductor but an electronic insulator, the LiAlO₂ interface layer can effectively suppress Li dendrite growth and the severe interface reaction between Li and Li₁₀GeP₂S₁₂. The Li@LiAlO₂ 200 nm/Li₁₀GeP₂S₁₂/Li@LiAlO₂ 200 nm symmetric cell can remain stable for 3000 h at 0.1 mA cm^-2 under 0.1 mAh cm^-2. Moreover, unlike the rapid capacity decay of a cell with a pristine lithium negative electrode, the Li@LiAlO₂ 200 nm/Li₁₀GeP₂S₁₂/LiCoO₂@LiNbO₃ cell delivers a reversible capacity of 118 mAh g^-1 and a high energy efficiency of 96.6% after 50 cycles. Even at 1.0 C, the cell with the Li@LiAlO₂ 200 nm electrode can retain 95% of its initial capacity after 800 cycles.

In situ artificial solid electrolyte interface engineering on an anode for prolonging the cycle life of lithium-metal batteries

Lithium, with its high theoretical capacity and low potential, has been widely investigated as the anode in energy storage/conversion devices. However, their commercial applications always suffer from undesired dendrite growth, which forms in the charging process and may puncture the separator, leading to short cycle lives and even security problems. Herein, by an in situ displacement reaction using SnF₂ at room temperature, we constructed an artificial solid electrolyte interface (ASEI) of LiF/Li-Sn outside the Li anode. This hybrid strategy can induce a synergy between the high Li⁺ conductivity of the Li-Sn alloy and good electrical insulation of LiF. Moreover, extreme synergy can be achieved by moderating the thickness of the LiF/Li-Sn ASEI, guiding dendrite-free lithium plating and stripping. As a result, a Li//LiFePO₄ battery that is assembled from the LiF/Li-Sn ASEI-engineered Li anode can obtain 1000 cycled lives with 86.3% capacity retention under a charge/discharge rate of 5 C. This work provides an alternative way to construct dendrite-free lithium metal anodes, which significantly benefit the cycle lives of LMBs.

Long-Lifespan Lithium Metal Batteries Enabled by a Hybrid Artificial Solid Electrolyte Interface Layer

Lithium metal batteries based on metallic Li anodes have been recognized as competitive substitutes for current energy storage technologies due to their exceptional advantage in energy density. Nevertheless, their practical applications are greatly hindered by the safety concerns caused by lithium dendrites. Herein, we fabricate an artificial solid electrolyte interface (SEI) via a simple replacement reaction for the lithium anode (designated as LNA-Li) and demonstrate its effectiveness in suppressing the formation of lithium dendrites. The SEI is composed of LiF and nano-Ag. The former can facilitate the horizontal deposition of Li, while the latter can guide the uniform and dense lithium deposition. Benefiting from the synergetic effect of LiF and Ag, the LNA-Li anode exhibits excellent stability during long-term cycling. For example, the LNA-Li//LNA-Li symmetric cell can cycle stably for 1300 and 600 h at the current densities of 1 and 10 mA cm^-2, respectively. Impressively, when matching with LiFePO₄, the full cells can steadily cycle for 1000 times without obvious capacity attenuation. In addition, the modified LNA-Li anode coupled with the NCM cathode also exhibits good cycling performance.

Role of Interfaces in Solid-State Batteries

Solid-state batteries (SSBs) are considered as one of the most promising candidates for the next-generation energy-storage technology, because they simultaneously exhibit high safety, high energy density, and wide operating temperature range. The replacement of liquid electrolytes with solid electrolytes produces numerous solid-solid interfaces within the SSBs. A thorough understanding on the roles of these interfaces is indispensable for the rational performance optimization. In this review, the interface issues in the SSBs, including internal buried interfaces within solid electrolytes and composite electrodes, and planar interfaces between electrodes and solid electrolyte separators or current collectors are discussed. The challenges and future directions on the investigation and optimization of these solid-solid interfaces for the production of the SSBs are also assessed.

Dual Protection of a Li-Ag Alloy Anode for All-Solid-State Lithium Metal Batteries with the Argyrodite Li6PS5Cl Solid Electrolyte

All-solid-state lithium metal batteries (ASSLMBs) are considered promising candidates for next-generation energy storage systems. However, the growth of Li dendrites and interface side reactions hinder the practical application of ASSLMBs. To address these issues, a preformed Li-Ag alloy anode for an ASSLMB with the Li₆PS₅Cl electrolyte was constructed. The preformed Li-Ag alloy anode contains two distinct alloy layers, i.e., Li₃Ag and Li_0.98Ag_0.02, with the former as a protection layer and the latter as a Li deposition site. Besides, a beneficial stable interlayer (Ag-P-S-Cl compound) produced by the reaction between Ag and Li₆PS₅Cl could work as a secondary protection layer between the anode and electrolyte. The dual protection (Li₃Ag and Ag-P-S-Cl compound) suppresses dendritic growth and other interfacial issues effectively and simultaneously. Consequently, a LiCoO₂/Li₆PS₅Cl/Li-Ag all-solid-state battery exhibits a remarkable specific capacity and excellent cycle stability. The dual-protection effect from the preformed Li-Ag alloy anode and the investigation of its working mechanism may enlighten a simple strategy for promoting the development of ASSLMBs.

New Insights into the Effects of Zr Substitution and Carbon Additive on Li3-xEr1-xZrxCl6 Halide Solid Electrolytes

Halide solid electrolytes have been considered as the most promising candidates for practical high-voltage all-solid-state lithium-ion batteries (ASSLIBs) due to their moderate ionic conductivity and good interfacial compatibility with oxide cathode materials. Aliovalent ion doping is an effective strategy to increase the ionic conductivity of halide electrolytes. However, the effects of ion doping on the electrochemical stability window of halide electrolytes and carbon additive on electrochemical performance are still unclear by far. Herein, a series of Zr-doped Li_3-xEr_1-xZr_xCl₆ halide solid electrolytes (SEs) are synthesized through a mechanochemical method and the effects of Zr substitution on the ionic conductivity and electrochemical stability window are systematically investigated. Zr doping can increase the ionic conductivity, whereas it narrows the electrochemical stability window of the Li₃ErCl₆ electrolyte simultaneously. The optimized Li_2.6Er_0.6Zr_0.4Cl₆ electrolyte exhibits both a high ionic conductivity of 1.13 mS cm^-1 and a high oxidation voltage of 4.21 V. Furthermore, carbon additives are demonstrated to be beneficial for achieving high discharge capacity and better cycling stability and rate performance for halide-based ASSLIBs, which are completely different from the case of sulfide electrolytes. ASSLIBs with uncoated LiCoO₂ cathode and carbon additives exhibit a high discharge capacity of 147.5 mAh g^-1 and superior cycling stability with a capacity retention of 77% after 500 cycles. This work provides an in-depth understanding of the influence of ion doping and carbon additives on halide solid electrolytes and feasible strategies to realize high-energy-density ASSLIBs.

First-principles simulation insights of electronic and optical properties: Li6PS5Cl system

We perform the electronic and optical properties of the Li6PS5Cl compound using first-principles calculation.